Manufacture of sponge iron



' y 0. M. H. GWYNN 2,509,921

MANUFACTURE OE SPONGE IRON Filed Nov. 30, 1945 3 Sheets-Sheet l lNVENTOR jllan'bm ll Gag 1m BY My, 9 M

ATTORN EYS Pmnaa a, 343 1950 MANUFACTURE OF SPONGE IRON Marion 1!. Gwynn, Mountain Lakes, N. 1., assignor, by mesne assignments, to Benjamin Clayton, Houston, Tex., doing business as Refining Unincorporated Application November 30, 1945, Serial No. 632,077

1 Qlaim. (Cl. 13-27) Some of the reasons for this are the necessity of employing extremely pure iron ore and the high cost of available reducing agents as well as the difficulty of controlling the heating of the iron ore and reducing agents to bring these materials to a desired reaction temperature without over-- heating. Nevertheless, the high quality of the iron or steel produced and the low temperatures at which the process can be carried on, as compared to blast furnace operations, has kept the problem of economically producing sponge iron continually before the industry.

In accordance with the present invention, the ore is carried to its final reduced state at relatively low temperatures by reaction with relatively pure hydrogen and a portion of the heat is supplied to the reaction zone by induction heating to generate heat directly in the particles of iron or iron ore. At leastthe final portions of the process are carried out under elevated pressure so that improved contact between the reducing gas and the partially reduced ore is accomplished. The process is preferably carried out continuously as the ore is rapidly reduced and a relatively large throughput can be produced in apparatus of small size. Since the materials entering the final reduction zone are at least partly preheated, the load on the induction heating apparatus is small and the induction heating apparatus functions largely as a temperature control. Although the entire reduction operation can be carried out in a single zone in which induction heating is employed, it is advantageous to partly reduce the ore by employing an impure and less expensive hydrogen containing gas and complete the reduction with relative pure hydrogen.

An object of the invention is therefore to provide an improved process of reducing iron ore in solid form with a gaseous reducing agent.

a screw conveyor 14 from a hopper it.

Another object of the invention is to provide ore is reduced in solid form by the employment of a gaseous reducing agent and supplying at least a portion of the required heatto the ore by induction heating.

Another object of the nvention is to provide an improved process of making sponge iron in which the iron ore is partly reduced with impure hydrogen and the final reduction is carried out with .relatively pure hydrogen under pressure.

Another object of the invention is to provide an improvedapparatus for reducing divided iron ore in which induction heating is employed for furnishing a part of the heat required to maintain the reaction temperature.

A still further object of the invention is to provide an apparatus for reducing solid iron ore with a gaseous reducing agent in which the ore is passed through refractory insulating tubes and heated therein by induction heating.

Other objects and advantages of the invention will appear in the following description of apparatus suitable for carrying out the invention and shown in the attached drawings of which:

Figure 1 is a diagrammatic view partly in section of a portion of an apparatus suitable for carrying out the present invention;

Figure 2 is a vertical section through a reduction chamber employinginduction heating;

Figure 3 is a horizontal section taken on the line.33 of Figure 2; and

Figure 4 is a schematic diagram of a system suitable for carrying out the present invention.

As shown in Figure 4, the major elements of the apparatus include a reducing furnace II! which may, for example, be of the conventional Herreshoif 'type through which the ore may be passed for partial reduction with impure hydrogen; a screening device II for separating dust or extremely fine material from the partly reduced ore; and one or more final reduction chambers I! for substantially completely reducing the ore to metallic form. The furnace Ill. shown in more detail in Figure 1, may have an ore inlet I3, the ore being fed to said inlet through The furnace It may be provided with a plurality of alternate shelves I1 and It, the shelves H extending inwardly toward the central portion of the, furnace and providing openings l9 adjacent duction chamber I2.

I chamber I9.

shaft 22 driven from any suitable source of power,

for example, through a gear 23. The shaft 22 may be provided with a plurality of rabble arms 24 positioned between the shelves I1 and I8 so that rotation of the shaft 22 causes downward progression of the ore through the furnace over the surfaces of the shelves I1 and I8. A reducing gas such as an impure hydrogen may be introduced into the bottom of the furnace I through a pipe26. This gas travels upwardly through the furnace in a zigzag path so as to pass through the ore on the shelves I1 and I8 and may be exhausted from the furnace through a pipe 21.

Partly. reduced ore may be delivered from the furnace through a conduit 20 into the interior of a rotary screen 29 positioned in a casing ill of the screening apparatus II, the rotary screen being mounted upon a shaft 32 driven from any suitable source of power through a gear 33. Fine material passes through the rotary screen 29 and may be discharged from the screening apparatus through a conduit 36 into any suitable receiver 31 (Fig. 4). The material retained on the screen 29 is delivered over the end 38 of the screen and discharged from the casing 3| through a conduit 39 which connects with branch conduits ii, 52 and 63 provided with valves or gates 46, ill and 48, respectively, in turn connected to storage chambers 49, 50 and respectively. These storage chambers areemployed to insure an even supply of partly reduced ore to thereduction chambers 82 and to act as pressure locks as will be hereafter described in more detail. The storage chambers 99, 50 and 5| may discharge through conduits 52, 53 and "54 provided with gates or valves 56, 51 and 58, respectively. The conduits 52, 53 and 54 all connect to a common conduit 59 which in turn connects with branching conduits 8i and 62, each connected to a re- If desired the portions of the conduits 6i and 62 connected to the chamber I2 may include screw conveyors (not shown) similar to the screw conveyor ill (Fig. 1) to regulate the feed to the reduction chambers 52.

The details of a reduction chamber 112 are shown in Figure 2. Such a reduction chamber may include a cylindrical pressure-tight casing 66 closed at its top end with an inlet structure 61 and at its bottom with an outlet structure 60'. The inlet structure 61 provides a header 68 for the upper end of a plurality of ceramic tubes 69 made of heat resisting electrical insulating material. The inlet structure also provides an ore feeding and gas separation chamber H and a central conically-shaped distributor 12 for directing the ore into thetubes 09. The chamber II is closed by a cover member 73 providing an ore inlet 14 to which one of the conduits 6| or 62 is connected. The cover member I3 also provides a gas outlet I6.

The lower closure structure 68' provide a header I'I for the lower end of the ceramic tubes 69 and in conjunction with a member I8 secured thereto provides an ore discharge and gas inlet Reducing gas is introduced into the chamber I9 through a circular manifold 8| connected to the chamber I9 through a plurality of pipes 82. The member 18 has a plurality of the ore is discharged into an ore discharge memher 94 by means of rotary arms 86 carried by a rotary member 81 mounted on a vertical shaft journalled in the header member 11 and discharge member 84, the shaft being driven at a relatively low speed from any suitable source of power through a gear 89. As shown in Figure 3. the ceramic tubes 69 are preferably arranged in a circle and are surrounded by an induction heating coil 9|, the coil 9| having its end extending through insulators 92 forming insulating and pressure-tight seals through the Walls of the easing 86 and also supporting the coil 9I.

Reduced ore is discharged from the reduction chambers through conduits 93 and 94 provided with valves or gates 96 and 9'I,- respectively, one of the conduits 93 and 94 being connected to a discharge member 84 of each reduction chamber I2. The conduits 93 and 94 are connected to a common conduit 98 which in turn is connected to branch conduits IOI, I02 and I03 provided with valves or gates I04, I05 and I06, respectively. .The conduits IOI, I02 and I03 are also connected to storage chambers I 01, I08, and I09, respectively, for reduced iron, the chambers I01, I08 and I09 being employed to insure a uniform feed to a briquetting apparatus III and as pressure locks for hydrogen gas in the system. The storage chambers I01, I08 and I09 are connected by conduits H2, H3 and H4 provided with gates or valves H6; I I1 and H8, respectively, with the briquetting apparatus I I I.

The reduction gas employed in the furnace I0 maybe a relatively impure gas such as coke oven gas. producer gas, etc.,.containing approximately or more hydrogen, the remainder being largely carbon monoxide. This gas may enter the system through a conduit H9 and be forced through the system by a Dump I2I. This ga is preferably first passed through a desulfurizer I22 for removal of sulfur. Such desulfurizers are .known in the art and the details thereof are not shown. The reducing gas may be discharged from the desulfurizer through a conduit I23 and passed through a heat exchanger I24 in which it is brought into indirect heat exchange relation with spent gas from the furnace I0. Partially heated gas from the heat exchanger may be delivered through a conduit I26 to a heater I21 in which the gas is brought to the desired temperature for introduction into the furnace I0 through the conduit 26. The conduit 26 may be connected to the interior of the screening device I I by means of a conduit I28 to maintain the same gas pressure in the screening device as is maintained in the furnace I0. Spent gas withdrawn from the furnace through the conduit 21 may be passed through the heat exchanger I24 in indirect heat exchange relation'with fresh reducing gas and then delivered through a conduit I29 to a cooler and condenser I30 employed to remove water vapor from the spent gas.' The water resulting from condensation of water vapor in the spent gas may-hadischarged from the cooler and condenser I30 through a pipe I3I. A portion of the cooled spent gas having water vapor largely removed therefrom may be recirculated through the furnace by means of a gas pump or compressor I32 in the conduit I33 connecting with,

the conduit I23. A substantial portion of the spent gas is, however, exhausted from the system through a conduit I34 provided with a regulating valve I36, the exhaustedgas being ordinarily used as a fuel to supply heat, for example, for heating the reducing gas in the heater I21.

The reduction gas employed" in the reduction chambers I2 will ordinarily be relatively pure hydrogen obtained from any suitable source. Such hydrogen enters the system through a conduit I81 and may be compressed in the gas pump or compressor I88 and then delivered to a heat exchanger I88 through a conduit I48. The fresh hydrogen is passed in indirect heat exchange with spent hydrogen from the reduction chambers I2 in the heat exchanger I 88 and delivered through a conduit I42 to a heater I48 in which the temperature of the hydrogen is raised to that desired in the reduction chambers I2. Heated hydrogen from the heater I48 is delivered through conduits I44 to the reduction chambers I2, one of the conduits I44 being connected to the manifold II of each reduction chamber I 2. In order to maintain substantially the same pressure on the interior and exterior of the ceramic tubes 88 of the reduction chambers I2, a pipe I48 may connect the conduit I44 with the interior of the casing 88 of the respective reduction chambers. The majority of the heat necessary for reduction in the reduction chambers I2 may thus be furnished by the heated hydrogen supplied thereto but a substantial portion of the heat necessary to reach reaction temperatures may be supplied from the induction heating coils 8I in the chambers l2. As shown in Figure 4, any suitable or known type of radio frequency generators I41 may be connected by "conductors I 48 to each of the induction coils 8|. The induction coils ill will ordinarily be constructed of copper tubing through which any desired cooling medium may be passed in accordance with conventional practice.

Spent hydrogen may be discharged from the reduction chambers I2 through gas outlets 18 of reduction chambers I2 connected to a common conduit I8I which delivers the spent hydrogen to the heat exchanger I88. The spent hydrogen is passed in indirect heat exchange with fresh hydrogen in the heat exchanger I88 and delivered through a conduit I82 to a cooler and condenser I88. Water vapor is condensed in the cooler and condenser I58 and the resulting water may be discharged therefrom through a pipe I84. The major portion of the' spent hydrogen after water vapor has been largely removed therefrom may be recirculated through the system. Thus, cooled spent hydrogen may be returned to the hydrogen inlet conduit I48 through a conduit I88 containing a pump or compressor I81. A small amount of hydrogen is continuously bled from the system through a conduit I88 provided with a regulating valve I88, the discharged hydrogen being ordinarily used as fuel to supply heat, for example, to the heater I48.

The storage chambers 48, 58 and 8| may be l and a pipe I88 having a valve I1|gtherein to a storage chambers 88 and II to the gas pressure of the reduction chambers before employing these chambers to feed the reduction chambers I2. Another of the storage chambers, for example, the chamber 88, may be in the process of being filled from a screening device II during withpipe I12 in turn connected to the lower pressure gas system of the furnace III, for example, to the pipe I28. Thus, when the storage chamber 48 is being employed to feed the reduction chambers I2, the valve 48 in its inlet ore conduit 4 I is closed' and the valve 88 in its outlet ore conduit 82 is open, the valves 81 and 88 in the conduits 88 and 84 being closed. Also, the valve I88 in the pipe I82 is opened to maintain the pressure in the,

storage chamber 48 substantially the same as that in the reduction chamber I2 and the valve I18 in the pipe connecting pipes I82 and I12 is closed to prevent loss of hydrogen to the low 4 pressure furnace system.

During this time, the storage chamber II may be receiving ore from the screening device II through the conduits 88 and", the valve 48 being opened. The storage chamber 8| may at this time have its pressure approximately the same' as that in the furnace I8 by being connected through the pipe I88, open valve I14 and pipe I12 to the conduit I28, the valve I88 being closed. It is assumed that the storage chamber 88 has been previously filled from the screening device II. By closing valve HI and opening valve I81, this storage chamber may be brought to the pressure existing in the reduction chambers I2 so that it is ready to be employed to feed the reduction chambers I2 by opening the valve 81, feed from the storage chamber 48 being simultaneously discontinued by closing the valve 58. Storage chamber 48, is then ready to receive partially reduced ore from the screening device as soon as the pressure therein has been reduced and storage chamber 5| has been filled. It will be seen that one of the storage chambers can be employed as a source of partially reduced ore for the reduction chambers I2 while another stor-' age chamber is being filled and the third chamber is being brought to the correct pressure depending upon whether it is to receive ore from the screen II or discharge ore to the reduction chamber I2. Thus, the chambers 48, 58 and 8| 60 bers I2 to prevent continuous leakage of high used successively to supply partially reduced ore to the reduction chambers I2. The, particular storage chamber supplying the reduction chambers I2 is maintained under the same gas pressure as the reduction chambers. In order to accomplish this, the, chamber being used as the feed to the reduction chamber, for example the chamber 48, may be connected to the conduit I8I for spent hydrogen through a pipe I8I and a pipe I82 having a valve I88 therein. The other storagechambers 88 and 8| may be provided with pipes I84 and I88 connected thereto and having valves I81 and I88, respectively, for also connecting these pipes to the pipe I" to bring the pressure hydrogen from the reduction chambers I2 into the low pressure system of the furnace I8.

.The briquetting apparatus III, which may be any known or suitable apparatus for this purpose is ordinarily operated at substantially atmospheric pressure and the storage chambers I81, I 88 and I88 may be employed in substantially the same manner as the storage chambers 49, 58 and SI. Thus, the storage chambers I81, I88 and I88 are provided with pipes I18, I18 and I8I, re

spectively, connected thereto, these pipes being provided with valves I82, I88 and I84 establishing communication with a pipe I88 connected to the pipe I48 from the compressor I38. The pipes I18,

78 I18 and I8I may also be connected with a pipe I81 its pressure adjusted to the desired pressure, these chambers also functioning as pressure locks for the reduction chambers I2 to prevent continuous leakage of hydrogen to the briquetting apparatus.

The amount of ore passed through the furnace I is primarily determined by the speed of rotation of the shaft 22. The screening apparatus I I should be of sufficient capacity to handle all of the ore fed from the furnace I0. The amount of ore passed through the reduction chambers I2 is primarily determined by the rotation of the shafts 38 thereof. Thus, the speeds of rotation of the shafts 22 and 88, all of which are rotated at relatively low speeds, should be correlated to maintain the amount of ore passing through the furnace lp siibstantially the same as the amount of ore passed through the reduction chambers I2.

As stated above, a relatively impure gas such as coke oven gas or producer gas can be employed for partial reduction in the furnace I0. In general,

the temperature in the furnace I0 will range between 1000 and 1100 F. although in some cases temperatures between approximately 900 and 1200" F. may be employed. It is preferred to partiallypreheat the ore entering the furnace I0 by any known or suitable means, the remaining heat necessary to bring the ore and gas to reaction temperatures being supplied by heating the reduction gas. The reduction gas ordinarily enters the furnace at a temperature between ap-' proximately 1200 and 1300 F. The heat of this gas in conjunction with any heat contained in the ore entering the furnace maintains the reaction temperature and compensates for radiation and other heat losses from the furnace I0. The furnace I0 is ordinarily operated at substantially atmospheric pressure or at most a few pounds per square inch above atmospheric pressure in order to retard decomposition of carbon monoxide with resulting deposition of carbon powder and-under these conditions it is relatively easy to maintain "'the reaction temperature in the furnace I0 at or near the desired reaction temperature.

It is desirable to maintain the ore during partial reduction and, while in'the partially reduced state, out of contact with the atmosphere. The screening apparatus II is therefore substantially closed from the atmosphere and kept filled with reducing gas by the conduit I28. To prevent building up excessive amounts of carbon monoxide in the reducing gas, a substantial portion of the spent reducing gas is discharged from the process through the pipe I34. For example, amounts of spent reducing gas ranging from 40 to 60% of this gas will be discharged and used as fuel, the remaining being recycled through the process through the conduit I33.

Thespartially reduced ore is discharged from the furnace .at a "temperature -betiv'en approximately 1000 and 1100 F. and although there is some reduction in the temperature of. ,the ore in the screening apparatus II and storage chambers 49, 50 and 5| due to heatiradiatiom'it is preferred the reduction chambers I2 as near these temperatures as practicable. On entering the reduction chamber through the inlet II, the partially reduced ore falls upon the distributor I2 and is directed into the ceramic tubes 69. This ore passes downwardly through the tubes 69 and is received in the chamber 19 from which it is discharged through the apertures83 at a rate controlled by the rotating arms 85. Reducing gas in the form of substantially pure hydrogen, after being heated in the heat exchanger I39 and heater I43, is introduced into the chamber I9 through the pipes 82'. The incoming hydrogen passes upwardly through the tubes 6! countercurrent to the movement of ore and.then separates from the ore in the inlet chamber II. The spent hydrogen is exhausted through the outlet I6 and then passes in indirect heat exchange with the incoming gas in the, heat exchanger I39 after which it is treated to remove water vapor in the cooler and condenser I53, most of the hydrogen being returned to the process through the conduit I56. A small portion of this gas, for example, 5 to 10% is discharged from the process through the conduit I58 in order to prevent the building up of impurities in the-system.

The ore entering the reduction chambers I2 is ordinarily at a relatively high temperature and the reducing reaction is endothermic. Also the reducing gases are heated before introduction into the reduction chambers I2. Very accurate temperature control is, however, required in order to produce substantially complete reduction of the ore while avoiding sinteringthe exact temperature to be employed for best results varying with the nature of the ore being reduced. It is, of course, possible to obtain a sufliciently high temperature in the reduction chamber I2 by preheating the ore or reduction gases or both, but it is extremely diificult to maintain a desired reaction temperature under such conditions. By employing induction heating to generate, directly in the particles of the partially reduced iron ore, a

substantial portion of the heat required to bring the ore to the desired temperature, very accurate temperature control can be obtained. That is to say, the generation of heat by induction heating can be instantly stopped when the temperature starts to rise above the desired temperature and immediately again started when the temperature begins to drop. By using a relatively low radio frequency, for example, a frequency between kc. and 1000 k0,, the magnetic field developed by the coil 9| penetrates substantially uniformly throughout the ore mass in the tubes 69 to provide substantially uniform heating. The exact frequency employed will depend upon the electrical conductive properties of the particular'particles being treated and their size so that the optimum frequency for a given installation will ordinarily be determined empirically. In some cases, it may be possible to employ frequencies as low as 15 kc.

The final reduction stage in the reduction chambers I2 is preferably carried on at elevated pressures, for example, pressures between 30 and 40 atmospheres. At these pressures, a relatively slow flow of gas can be employed so that the gas can be readily separated from the ore in the inlet chamber II. Also, the higher pressures promote contact between the ore and the reducing gas and by employing relatively'pure hydrogen, n0

deposition of carbon is produced. The ceramic 9 tial pressure as the interior of the casing II is maintained at substantially the same pressure as the interior of the tubes 08. The external pressure will, in general, be somewhat larger than the internal pressure due to the friction drop of gases passing through the ore but any slight leakage of gas into the tubes or the chambers II or The temperature of reaction in the reaction chambers [2 will ordinarily fall between 1000 and 1100 F. although in some cases temperatures as low as 900 F. and in other cases as high as 1200" F. may be employed. The maximum tem-- perature employed must be below that at which substantial sintering is produced in order to prevent blocking or "hanging" of ore in the tubes although slight sintering can be tolerated as the adhered particles will ordinarily be separated by the rotating arms '06 in the discharge chamber 19 of the reaction chamber. These arms keep the ore in constant movement through the tubes 09 to prevent the blocking or hanging referred to above. Also, the tubes 69 are preferably construced to have a slight internal taper so that their internal diameter is somewhat larger at the bottom or discharge portion of the tubes than it is at. the top or inlet portion of the tubes. This taper in conjunction with the intermittent agitating action of the arms 88 of the rotary member I! as they pass below the discharge openings of the tubes 88 is, with most ores, sufficient to prevent blocking of the powdered ore in the tubes so that the ore moves substantially uniformly through the tubes.

Certain ores may exhibit a pronounced tendency to resist uniform fiow through the tubes due to partial sintering or other causes, in which case any known or suitable means may be employed to prevent blocking of the tubes. For example, rotary or reciprocable rods of ceramic or other heat resisting insulating material may extend into or through the tubes and be arranged for intermittent or substantially continuous movement, for example, from the rotating member 81, to agitate the ore in the tubes and maintain it in substantially uniform movement therethrough. Alternatively, the entire reaction chamber I! may be positioned horizontally or at an inclination to the horizontal with the discharge end lower than the inlet end, and suitably driven rotating screw or similar members made of ceramic or other heat resisting insulating material employed to.

advance the ore through the tubes.

'It theoretically requiresapproximately 16,000 cubic feet of hydrogen at atmospheric pressure to reduce a ton of iron ore but in practice approximately 18,000 to 20,000 cubic feet of hydrogen are required since all of the hydrogen can not be effectively employed. By partially reducing the ore with impure hydrogen as disclosed above, the amount of substantially pure hydrogen can be materially reduced, the cost of pure hydrogen being largely the determining factor in the cost of the process. Thus, from 50% to 70% of the reduction can be rapidly and easily produced in the furnace ID by employing relatively cheap impure hydrogen and the final reduction accomplished by relatively pure hydrogen. It is extremely diflicult, if not impossible, to substantially completely reduce the ore .with inexpensive impure hydrogen. By the operation described above, the pure hydrogen demand per ton of ore may, however. be-reduced "from 50 to 70% from that required when pure hydrogen isemployed throughout the process. In the present process both the-partial reduction in the furnace I0 and the substantially complete reduction in the chambers l2 are rapid operations so that the throughput of the combined process is much greater than would be the case if the entire reduction were carried on in either major step even though the size of the apparatus for either of these steps were increased commensurably.

Ore in relatively finely divided form, the condition inwhich iron ore concentrates are usually obtained, can be effectively handled in the present case. The furnace II! can handle ore as fine as 200 mesh, although a coarser ore, .for example, 10 to 60 mesh is more easily handled. An ore which is predominantly 40 to 60 mesh is best handled by the furnace l0 although-a substantialportion of finer ore may be present.j The reduction chambers H can also handle relatively fine material as the tubes 69 may be relatively short so that the gas pressure diilerential between the ends of the tubes is not excessive. Due to the agitation of the ore in the furnace l0, 9. small amount of extremely fine material is produced and this tends to retard gas flow through the tubes 69 in the reduction chambers l2.- The screening apparatus II should therefore remove substantially all ore particles which are less than 200 mesh.

It is entirely possible to carry out the entire reduction process in the reduction chambers I2 in which case the primary reduction furnace l0 can be eliminated. Even so, the amount of heat required to be introduced into the ore by induction heating is small. Iron ore particles are, in general. of suificient electrical conductivity to be subject to induction heating by an alternating magnetic field, and in any case the reduction chambers I2 can be initially charged with partially reduced ore so that fresh ore entering the chambers is partially reduced by hot reducing gases passing therethrough before entering the magnetic field. By employing the heat exchanger I39, preheating the ore and insulating the reduction chambers as far as possible against loss of-heat by radiation, the process of the present invention can be successfully carried out even with no partial reduction of ore before it is introduced into the reduction chambers l2. The

induction heating is employed primarily as a temperature control for the process. By varying the electric power supplied to the heating coils ill in accordance'with the temperature of the ore in the reduction chambers, a substantially constant reaction temperature may be maintained therein. I

While I have disclosed the preferred embodiment of my invention, it is understood that the details thereof may be varied within the scope of the following claim.

I claim:

Apparatus for reducing finely divided ore, which comprises, a pressure chamber, a plurality of vertically extending ceramic tubes positioned in said pressure chamber, upper and lower headers for said tubes, means for passing ore through said tubes, means for passing a reducing gas under pressure through the ore in said tubes and for maintaining a gas pressure in said pressure chamber substantially equal to the pressure of the gas in said tubes, an induction coil supported in 11 rent power to said inductloncoll to generate heat Number Name M in the particles of said ore.- 2,144,618 Clark Ja 24, 1939 MARION H. GWYNN. 2,166,207 Clark July 18. 1939 2,236,474 Hardy Mar. 25, 1941 REFERENCES CITED 5 2,243,110 Madaras May 21, 1941 v The following references are of record in the 2,266,003 Clark D c. 1 1 41- file of this patent: ghrfnwald jlfyeyzg, 1:22 a a a 11 2 STAIES mus, 2,338,606 Voorhees Jan.4,1944 Number Name Date 10 2,359,578 Payne -1 Oct. 3, 1944 764.044 Diesler July 5, 1904 2,455,092 Ramseyer N v; 30, 19 1,090,874 Pier Mar. 24. 1914 i 1,286,135 Somermeier Nov. 26, 1918 OTHER REFERENCES 1759173 smith May 1930 Transactions of the American Institfitg of M1 n 41 Arnold June 1938 15 in: and Metallurgical Engineers, vol, 135, pages.

2,142,100 Avery 1939 58-72 (1939) 

